On the origin of the strong internal magnetic fields of central compact objects

TL;DR

This paper investigates the origin of strong internal magnetic fields in central compact objects, suggesting they inherit their dipole fields from progenitors and generate strong toroidal fields during the proto-neutron star stage, without significant dynamo activity.

Contribution

It proposes a model explaining the internal magnetic field strengths of central compact objects based on flux conservation and the Omega-effect, without relying on dynamo processes.

Findings

Dipole fields are inherited from progenitor cores.

Strong toroidal fields can be generated via the Omega-effect.

These objects are born slow-rotating due to lack of spin-up from fallback matter.

Abstract

Central compact objects are radio-quite young neutron stars associated with supernova remnants. They have relatively small dipole fields, $B_{\rm p} \sim 10^{10}\,{\rm G}$ as inferred from their spin parameters. X-ray observations and theoretical arguments imply the presence of stronger internal magnetic fields. We argue that the dipole fields of these objects are very close to what they had inherited from the \textit{core} of the progenitor by flux conservation and their small initial rotation frequency does not allow for the $\alpha$-process to enhance their poloidal fields. Although a full-fledged dynamo process can not proceed, relatively strong toroidal magnetic fields, $B_\phi \sim 10^{13}\,{\rm G}$, can be generated from the seed poloidal fields via the $\Omega$-effect in the proto-neutron star stage. We present a simplistic model for these processes and further speculate that the reason why these objects are born relatively slow-rotating is that they were not spun-up by acquiring angular momentum from the fallback matter.